MoCrFeMnNi高熵合金退火后的组织和性能

高熵合金因具有高强度、耐腐蚀、耐高温氧化等优异的性能而备受关注.采用铝热反应法制备MoCrFeMnNi高熵合金,用XRD、SEM、EDS、显微硬度和压缩实验研究了铸态及700 ℃/12 h、800 ℃/6 h、1 000 ℃/3 h退火后合金的组织和性能变化.结果表明:铝热法制备的MoCrFeMnNi高熵合金为典型的枝晶形貌,晶体结构主要由BCC相、FCC相以及少量的σ相构成,其中枝晶区域为BCC结构,富含Mo和Cr元素;枝晶间区域为FCC结构,富含Ni元素.随着退火温度的上升,枝晶间逐渐析出纳米级σ相,使得合金硬度上升,在800 ℃/6 h退火处理后达到667 HV,抗压强度达到1 050 MPa;1 000 ℃/3 h退火后,σ相团聚成球状和针状并在高温下部分溶解,σ相的减少使得合金硬度下降,抗压强度与铸态时相当,塑性显著提升.

Microstructure and properties of annealed MoCrFeMnNi high entropy alloys

High entropy alloys have attracted extensive attention due to their high strength, corrosion resistance and high temperature oxidation resistance. In our research, a high-entropy alloy MoCrFeMnNi was prepared by aluminothermic reaction method. Microstructures and properties of 700 ℃/12 h, 800 ℃/6 h, 1 000 ℃/3 h annealed alloys were investigated respectively by XRD, SEM, EDS, microhardness test and compression experiment. The results show that the high entropy alloy MoCrFeMnNi prepared by the aluminothermic method has typical dendritic morphology, and the crystal structure is mainly composed of BCC phase, FCC phase and a small amount of dispersion phase. The dendritic region is BCC structure, rich in Mo and Cr elements. The interdendritic region is FCC structure, rich in Ni element. With the increase of annealing temperature, the nanoscale σ phase is gradually precipitated between dendrites, leading to the increase of alloy hardness, which may reach up to 667 HV and 1 050 MPa after annealing at 800 ℃/6 h. After annealing at 1 000 ℃/3 h, the σ phase agglomerates into a spherical and acicular shape and is partially dissolved at high temperature. With decrease of σ phase, the hardness of the alloy decreases, the compressive strength is equal to that of as-cast state, and the plasticity of the alloy is significantly improved.